Why no more lean burn??

[jamiec]

I had the pleasure of a couple visits to Australia in the late 1990s. The Early Ford Owners Club of Tasmania too us on a tour of their island and the topic of the strict laws came up. I was surprised at how difficult the import process was with the manadory right hand drive conversion.

We don't have to convert to right hand drive anymore.

[cujet]

Those who have aftermarket, stand-alone engine management computers have done some interesting things with lean operation on very modern engines.

Lean operation requires more throttle opening, and the throttle by wire can compensate without driver input. Driveability issues are minimized with such setups.

My current "fun" car is a 2004 Turbo S2000 with stand-alone ECU, 8.8/1 compression, 19.5Lbs boost. It does not run lean under light loads, and does not return very good MPG's. (about 20) . My plan is to re-map the ECU for 17/1 operation under light loads. Those that have done this see overall increases to 25 to 27MPG.

It's my understanding that modern direct injection engines have been configured to operate smoothly at much leaner A/F ratio's. And coupled with high compression, can achieve BSFC numbers almost 25% better than the very same engine operated at stoic.





Take a look at the lower picture. That's my 1971 Cessna 177RG. I'm operating it in very lean mode! (GAMI injectors and other tweaks) I'm achieving a solid 25MPG at 125MPH. I promise, there is no tailwind and I'm actually climbing in this pic. What I do is lower the RPM to 1900-2000, pull throttle to 17 inches manifold pressure and lean it to it loses significant power and misfires a touch, then richen it just a touch. I then fiddle with the controls to achieve a bit less than 5 gallons per hour fuel flow. (the gauge is just to the right of my iPad)

Note: in non lean operation, the same speeds consume about 8GPH.



Look at the airspeed indicator, 113MPH at 4500 feet. That's 125 true airspeed. (remember, the higher you go, the lower the airspeed indicator is for a given speed, due to thin air)

[Bindegal]

As near as I can tell, the 1996-2001 Civic 1.5iLS D15Z6 runs AFR 20-22.
(no clue what it´s called in the US if it exists)

Note you´ll likely need an LSU4.9 wideband to read this lean

/Allan

[iveyjh]

I can run my Metro on lite cruise at 22-1+ without a miss but power drops off. My wide band gauge will read 22.4 but I can run leaner.

[steffen707]

Originally Posted by Old Tele man

Not really, as the Air Fuel Ratio (AFR) is still the ratio of AIR-to-GASOLINE, except with Direct Injection (DI) it occurs *instantly* within the cylinder when the injector pintle opens and injects a specfically-metered amount of GASOLINE into the compressed AIR inside the cylinder...it's still a ratio.

With DI, AFR can become more dynamic, but only *IF* the Engine Control Module (ECM) "brain" is smart enough to make "right" changes rather than just "some" changes...which boils down to intelligent algorithms and software/firmware inside the ECM. Thus, some manufacturers will have it, some won't.

The *problem* comes back to what's coming OUT of the exhaust pipe, and DI (as currently implemented) has been shown to INCREASE exhaust particle pollutants...and, particles "plug" catalytic converters.

And, NOx scrubbing isn't currently *up* to meeting current EPA emission requirements, much less, the anticipated FUTURE requirements coming down the pike. So, *lean-burn* (AFR ~ 16-18:1 or more) is not likely to come-back soon, without new break throughs in both DI and catalytic converters...ie: probably something like urea purge injection, etc.

My 96 civic with vx drivetrain didn't make enough power in lean burn to maintain 65mph, only about 55-60 with careful attention to the gas pedal. Albeit, a 92-95 hatch had better aero and probably does maintain 60-65mph in lean burn.

Anyways, I drive a jetta tdi now. Aren't all diesels lean burn? Do they have high NOX? And with urea purge injection, could you take a gas lean burn engine and reduce its NOX to a safe level? I think you get direct injection with lean burn and hybrid setup and you're set. ......wait, that's what the first gen insight was right?

[cbaber]

Originally Posted by Old Tele man

Q: Why no more lean burn??

A: EPA regulations.

Notice how "Best Economy" (blue line, ie: Lean Burn) coincides with NOx peak in below graph...and, remember, it's NOx which creates LA's brown-smog.



• source: EndTuning - Air Fuel Ratios

If this graph is true, lean burn can actually reduce fuel economy & emissions. Notice the peak nox occurs around 16 on the A/F scale, but Honda lean burn applications run up to about 25:1. So if we run a lean burn of 18:1 not only are we using less CO2 and nox than regular burn, we are using much less fuel.

So it really isn't valid to say that lean burn is banned because it creates more nox, when clearly at certain ratios it actually produces less emissions and returns higher MPG. Or am I reading the graph wrong?

[Daox]

In that graph, NOx starts coming down, but HC (hydrocarbons, or gasoline) start going up because of misfiring.

I'm not exactly sure where that graph comes from. I believe its from a Toyota paper. Its obviously from some engine, and an engine designed for lean burn obviously isn't going to misfire at 18:1. So, you may be right, but we can't really know for sure because we don't have details on it.

[Bindegal]

Is it known if the graph represents emissions output before or after the cat? (my guess is before)
It seems to me like many modern cars run AFR 14.7 / lambda 1.0 as often as possible. Even at WOT until very high RPM. Basically sacrificing economy and power for catalytic converter efficiency in keeping emissions down.

[RustyLugNut]

Originally Posted by Bindegal

Is it known if the graph represents emissions output before or after the cat? (my guess is before)
It seems to me like many modern cars run AFR 14.7 / lambda 1.0 as often as possible. Even at WOT until very high RPM. Basically sacrificing economy and power for catalytic converter efficiency in keeping emissions down.

I have seen similar graphs in various texts that go back to the 70's. It is an example of engine out emissions before any remediation techniques are applied to an "average" engine.

And, you are correct that most modern cars sacrifice performance/economy for emissions.

[tony_2018]

It comes down to the catalyctic converter, thats what cost so damn much. Its not your typical cat converter.